Low-Frequency Current Injection for Sensorless Control of Multiphase Induction Machines at Zero and Very Low Speeds

This article introduces a sensorless control strategy for a seven-phase induction motor drive, leveraging the inherent degrees of freedom in multiphase systems. The proposed approach relies on injecting a low-frequency current to excite the third spatial harmonic of the magnetic field in the air gap. This excitation facilitates the estimation of the third spatial harmonic component of the flux linkage. The injection of a low-frequency current enables the estimation of the rotor flux position at zero and very low speeds without torque ripple, which is an essential requirement for the reliable operation of sensorless drives. The experimental tests conducted under different operating conditions confirm the robustness of the proposed solution, as well as its dynamic response and stable behavior at zero and low speeds.